A way by which a web browser takes a user from one page to another without the user clicking or making any input.
This type of redirect is to be used for permanent redirects (example: you own websiteA.com and websiteB.com but you only want one website.
There are various types of redirects (the most common of which is the 301 redirect), which serve different purposes. You would 301 redirect all of the traffic from websiteB.com to websiteA.com so that all visitors end up on websiteA.com)
Typically, this helps improve user experience across a website by helping the user find what they are looking for or avoiding dead ends like 404 (Not Found) errors.